Virtual Leased Line (VLL) is a service for providing Ethernet based point to point communication over Internet Protocol (IP) and Multi Protocol Label Switching (MPLS) networks (IP/MPLS). This technology is also referred to as Virtual Private Wire Service (VPWS) or Ethernet over MPLS (EoMPLS). The VPWS service provides a point-to-point connection between two Customer Edge (CE) routers. It does so by binding two attachment circuits (AC) to a pseudowire that connects two Provider Edge (PE) routers, wherein each PE router is connected to one of the CE routers via one of the attachment circuits. VLL typically uses pseudowire encapsulation for transporting Ethernet traffic over an MPLS tunnel across an IP/MPLS backbone. More information on pseudowires can be found in “Pseudo Wire Emulation Edge-to-Edge (PWE3) Architecture”, RFC3985, IETF, March 2005, by S. Bryant and P. Pate.
Virtual Private LAN Service (VPLS) is an Ethernet service that effectively implements closed user groups via VPLS instantiations. In order to achieve full isolation between the user groups, VPLS dedicates a separate forwarding information base (FIB) on network routers per VPLS instance. Each VPLS instance further requires that a dedicated mesh of pseudowire tunnels is provisioned between PE routers that are part of the VPLS.
Both VLL and VPLS services use Service Access Points (SAP) to bind tunnel endpoints at PE routers ports to their respective service. For example, in the case of VPLS service a SAP would specify physical identifiers (e.g. node, shelf, card, port) of the corresponding port and an identifier (e.g. VLAN5) of the VPLS.
In order to offer highly reliable VLL and VPLS service it is necessary to protect against pseudowire tunnel failures, which for example could result from a failure at a PE router at either end of a pseudowire tunnel or any intermediate router through which the tunnel passes. Ideally, this protection would be in the form of automatic protection switching at a PE router to a redundant tunnel upon detection of a failure affecting a primary tunnel. Unfortunately, not all PE routers have the capability to provide this form of protection on all types of pseudowire tunnels. Therefore, a means of providing pseudowire tunnel redundancy that does not depend on the tunnel redundancy capabilities of a router is desired.